This invention relates generally to optical assemblies, and more particularly to assemblies including waveguides, for example optical fibers, in optical connection with high performance filters.
Optical assemblies including waveguides in recent years have been recognized as offering a high potential for solving problems in a number of commercial applications including telecommunications and medical diagnostics. Optical fiber assemblies are well known in telecommunications and have been found to be especially useful in analyzing materials by employing various types of light-scattering spectroscopy. Optical filters have been found to be useful in such applications. In telecommunications typical uses include bandpass filters in wavelength-division multiplexing and as noise blocking filters for optical amplifiers.
The term xe2x80x9cwaveguidexe2x80x9d is used herein to refer to an optical structure having the ability to transmit light in a bound propagation mode along a path parallel to its axis, and to contain the energy within or adjacent to its surface. In many optical applications it is desirable to filter light that is propagating within a waveguide, perhaps an optical fiber, in order to eliminate or redirect light of certain wavelengths or to pass only light of certain wavelengths.
Many types of filters, including interference filters, are commonly used for this filtering. However, there are a number of difficulties associated with the use of many types of filters, including interference filters. First, in some applications the power density of light propagating within a waveguide may be unacceptably high for the filter, having detrimental effects that may include damage to the filter material or reduced filter performance.
Also, filters are typically employed by means of bulky, multiple-optical-element assemblies inserted between waveguides, which produces a variety of detrimental effects. Separate optical elements can be difficult to align in an assembly and it can be difficult to maintain the alignment in operation as well. Each element often must be separately mounted with great precision and the alignment maintained. Also, an increase in the number of pieces in an optical assembly tends to reduce the robustness of the assembly; the components may be jarred out of alignment or may break. In addition, interfaces between optical elements often result in significant signal losses and performance deterioration, especially when an air gap is present in the interfaces. The materials of which the additional elements are composed may also introduce fluorescence or other undesirable optical interference into the assembly.
The size of filtering assemblies is often a problem as well. Not only can it be difficult to manufacture a filter on a small surface area, but also filtering assemblies usually contain bulky light-collimating, alignment and mounting components in addition to the filtering element. However, space is often at a premium in optical assemblies. In addition, the filtering characteristics of interference filters change depending upon the angle at which light is incident on the filter, and interference filters are generally designed for the filtration of normally incident light.
High performance filters have shown particular promise in many applications as described in Applicants"" co-pending U.S. patent application Ser. No. 09/267,258 and U.S. Pat. No. 5,953,477. There is an ongoing demand for assemblies in these and other industrial and medical applications that have less noise. In telecommunications the demand for more useable bandwidth is growing at an incredible rate. That telecommunications demand and the recognized need for more effective medical and environmental diagnostic tools (for example those described in the referenced U.S. patent application Ser. No. 08/819,979 now issued as U.S. Pat. No. 5,953,477) are resulting in the need for assemblies having improved signal to noise ratio.
This invention provides a surprisingly effective optical noise reduction in optical assemblies by controlling or limiting unwanted photon entrance, reflection, departure or appearance in or from the assembly. Applicants have found such unwanted photons passing through areas that had not been recognized or had been vastly underestimated as photon passageways potentially creating significant problems. Applicants have further found the optical performance loss because of these areas to present special, technology limiting problems in applications benefiting from high performance filters. More specifically, applicants have found that penetration of unwanted photons especially in areas along periphery of the filter layers, even very thin filter layers, can cause significant noise or effective signal erosion. This is especially true when optical transmission purity/high optical performance is essential. That unwanted photon penetration occurs not only through edge surfaces but also through face surfaces and edge junctures. The edge juncture is where the filter edge surface joins a filter face surface or a filter face surface joins another face, for example, of a waveguide, including an optical fiber. Problematic optical noise can occur through the filter face itself if, for example, some areas of the filter or the waveguide to which it is optically connected have differing transmission characteristics or demands. In accordance with this invention improvements are obtained by selectively covering with a material opaque to the unwanted photons those areas that would otherwise allow the unwanted penetrations. Assemblies according to one embodiment of the invention when used to cover such junctures can effectively be utilized as universal adapters for connecting fibers to one another or to optical devices for specific applications, for example, in chemical analysis and or communication facilitating devices. A fiber identification mechanism assures proper fiber matching and alignment.